Caliguey

Hi everyone, first time posting here. I have a 1996 Chevy Tahoe and there has been an off-and-on fairly loud knocking sound coming from my passenger side dashboard, near the glove box.

• This sound started after I had used the air-recirculation button for the first time in years.
• Sometimes it makes the sound, and other times it does not.
• The car just needs power, does not need to have the motor running for this sound to happen.
• The vents do not need to be on, it happens at the same frequency and volume no matter what the fan power setting is on. (Something to note is that my vents seem to blow air even when on the 'off' position, although it is a small amount)
• If I press the air-recirculation button while the sound is happening, it will stop for a small amount of time (<30 seconds) then continue at a slightly different frequency and volume.
• Additional to the previous one; if the air recirculation button is on but the vents are set to 'off', there is no change in the sound. The vents need to be switched at least to 'low' for the different frequency/volume to be obtained.
• My vents blow hot and cold air. There is not a problem switching the temperature mixer. AC hasn't been used in forever and the freon is not charged.

At first I thought it was just a blend door actuator but the fact that my temperature mixer works makes me doubt that. I'm going to take off my glove box and the next time the sound starts just start feeling on stuff and see whats ticking.
I am by no means a mechanic and any advice/opinions would be greatly appreciated.

Irish_alley

it could still be a blender door actuators. dont quote me but you either have 3 or 4. it could be the blender door actuators for the fresh air and thats why you have hot and cold air but it could also still be working and just showing its age. best thing is to find the actuators and put you hand on it and cycle through the settings to get it to pop or click.

Caliguey

Thanks for the reply. Ok, I'll give that a try.